Preheat the oven to o 350ºF. Lightly grease a cookie sheet and line with
parchment paper.

Place the butter and sugar in the bowl of a mixer fitted with
a paddle and mix until smooth. Scrape down he sides of the bowl, add the eggs
and vanilla, and mix until just combined, being careful not to overmix.

Scrape down he sides of the owl; add the flour, cocoa powder,
baking soda, baking powder, salt and, if desired, the nuts, and mix until
everything is well incorporated.

Place teaspoonfuls on the he prepared cookie sheet and transfer to the oven.
Bake until the edges begin to firm up, about 12-13 minutes. Do not overbake. For
crisper cookies, cool on the cookie sheet. For softer cookies, cool for 2
minutes and then remove to a rack. Cool the cookie sheets between batches.